Magnetization Relaxation and Collective Spin Excitations in Correlated Double--Exchange Ferromagnets

TL;DR

This paper introduces a non-perturbative Green's function method to study spin relaxation and collective excitations in correlated double-exchange ferromagnets, revealing how Coulomb interactions and carrier concentration influence spin dynamics.

Contribution

It develops a novel Green's function expansion that accurately captures correlations and relaxation processes beyond traditional approximations in ferromagnetic materials.

Findings

Coulomb interaction qualitatively alters spin-wave dephasing rates.

Spin relaxation depends on three-body correlations with electrons and holes.

Carrier concentration can control spin dynamics.

Abstract

We study spin relaxation and dynamics of collective spin excitations in correlated double--exchange ferromagnets. For this, we introduce an expansion of the Green's functions equations of motion that treats non--perturbativerly all correlations between a given number of spin and charge excitations and becomes exact within a sub--space of states. Our method treats relaxation beyond Fermi's Golden Rule while recovering previous variational results for the spin--wave dispersion. We find that the momentum dependence of the spin--wave dephasing rate changes qualitatively due to the on--site Coulomb interaction, in a way that resembles experiment, and depends on its interplay with the magnetic exchange interaction and itinerant spin lifetime. We show that the collective spin relaxation and its dependence on the carrier concentration depends sensitively on three--body correlations between a spin excitation and a Fermi sea electron and hole. The above spin dynamics can be controlled via the itinerant carrier population.